Intro/Purpose: Macromastia can be a morbid condition experienced by women who exhibit symptoms including shoulder pain, back pain, intertrigo, shoulder/brastrap grooving, and loss of function. However, efforts to objectify the medical necessity for reduction mammaplasty have been difficult. Therefore, to gain greater clarity regarding the efficacy of reduction mammaplasty surgery, this pilot study was conducted to determine the extent to which reduction mammaplasty surgery produces a change in biomechanical stress of the spine and level of disability in women with macromastia. Materials/methods: Eleven females (mean age: 44.18 ± 12.88; range: 27-71y; BMI: 32.1 ± 5.95) determined to need a medically necessary reduction mammaplasty surgery participated in a biomechanical analysis and responded to a questionnaire prior to and following their surgery (within one week of their scheduled surgery date and approximately 3 months [mean days: 87.09 ± 13.7] following their surgery). Biomechanical analysis included performance of 3-trials of a lifting task using a 5 lb. weight located 12 in. anterior to the feet and 16 in. above the ground. Concurrent kinematic and kinetic data from the task was collected using a 6-camera motion capture system (Vicon; Centennial, Co) and an in ground force-plate (AMTI; Watertown, MA). A custom made application (Matlab: Natick, MA) was used to calculate the total compressive forces at the low back using an inverse dynamic approach based on Zatiorsky's anthropometric data. Functional analysis consisted of the completion of the standardized Function Rating Index (FRI) questionnaire to assess their self-reported ability to perform dynamic movements of the neck and back and/or withstand static positions. Results: The average maximum low back compressive force during the lifting task decreased 35% post surgery (pre-test: 3,406.85 ± 1,429.39 Newtons, post-test: 2,199.82 ± 619.15 Newtons; p=0.004). Furthermore, scores on the functional rating index improved 76% (pre-test: 45.68 ± 17.29, post-test 10.91 ± 7.93; 0= no dysfunction, 100= severe dysfunction; p=0.002). Conclusions: Individuals who underwent reduction mammaplasty experienced decreased biomechanical stress in the low back. In addition, participants reported dramatic improvements in their ability to perform dynamic movements and withstand static positions. To our knowledge, this is the first study to objectively document reductions in biomechanical stress of the low back and disability as a result of reduction mammaplasty surgery. The results from this study combined with previous research demonstrate that women who undergo medically necessary reduction mammaplasty surgery may be at a decreased risk for disc degeneration and low back disorders. These results warrant additional research to prospectively investigate these individuals.